Switch or relay device for a ring network, the switch configured to detect and correct duplication of switch identifications

ABSTRACT

A relay device, or a switch, in a ring network corrects connection information including (i) identification information of respective switches in the network and (ii) a connection order of other switches seen from a subject switch, by storing in a memory a switch ID table of the subject switch, which includes an ID of each of the other switches and a connection order of the other switches seen from the subject switch, for identifying an abnormal section of the network, for example. Each of the switches has a function that (i) generates anew ID for the restarted switch for generating a new ID table and (ii) causes the other switches to generate a respective new switch ID table, when detecting switch ID duplication among the switches or when restarting from a reset.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on and claims the benefit of priorityof Japanese Patent Application No. 2019-134564, filed on Jul. 22, 2019,the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally relates to a switch or a relay devicein a ring network as part of an in-vehicle communication network.

BACKGROUND INFORMATION

In general, a ring network is a network topology in which each nodeconnects to exactly two other nodes, forming a single continuous pathwayfor signals through each node—a ring. Data travels from node to node,with each node along the way handling every packet. Rings can beunidirectional, with all traffic travelling either clockwise oranticlockwise around the ring, or bidirectional.

For example, in an Ethernet network, a ring topology is formed byconnecting a switches serving as relay devices in a ring shape (Ethernetis a registered trademark). In the ring topology, a plurality ofswitches (i.e., ring switches, or relay devices) are connected in a ringshape by two ports of each switch respectively connected to ports ofadjacent switches. The switches and communication lines connecting theswitches constitute a ring network capable of making a frame go aroundand come back (i.e., circulate the frame in/through the entire network).

Conventional problems include ID duplication and incorrectidentification of abnormal sections.

SUMMARY

It is an object of the present disclosure to provide a relay devicecapable of correcting connection information representing (i)identification information of other relay device(s) connected in a ringnetwork and (ii) a connection order of the other relay device(s) viewedfrom the relevant relay device.

A relay device according to one aspect of the present disclosure is usedin a communication system in which a plurality of relay devices areconnected in a ring shape. The relay device according to one aspect ofthe present disclosure is provided with a storage unit in which theconnection information is stored. The connection information indicates(i) identification information of other relay device connected in a ringshape and (ii) a connection order of the other relay device as viewedfrom a subject relay device.

BRIEF DESCRIPTION OF THE DRAWINGS

Objects, features, and advantages of the present disclosure will becomemore apparent from the following detailed description made withreference to the accompanying drawings, in which:

FIG. 1 is a diagram of a configuration of an in-vehicle communicationnetwork system according to a first embodiment;

FIG. 2 is a diagram of a configuration of an Ethernet frame;

FIG. 3 is a diagram of an example of a switch ID table;

FIG. 4 is a flowchart of a table generating frame transmission process;

FIG. 5 is a flowchart of a table generation process;

FIG. 6 is a flowchart of a first process;

FIG. 7 is a flowchart of a second process;

FIG. 8 is a flowchart of a third process;

FIG. 9 is a flowchart of a fourth process;

FIG. 10 is a flowchart of a fifth process performed in a secondembodiment;

FIG. 11 is a flowchart of a sixth process performed in the secondembodiment;

FIG. 12 is a flowchart of a seventh process performed in the secondembodiment; and

FIG. 13 is a flowchart of an eighth process performed in the secondembodiment.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described below withreference to the drawings.

1. First Embodiment 1-1. Configuration

An in-vehicle communication network system 1 according to the firstembodiment shown in FIG. 1 includes ECUs 11 to 22 and communicationlines 31 to 42 installed in a vehicle. The in-vehicle communicationnetwork system is, if simply called, an in-vehicle communication networkor a communication system. ECU is an abbreviation of “Electronic ControlUnit” representing an electronic control device. Examples of the ECUs 15to 22 include an automatic driving ECU and an image processing ECU.

The ECUs 11 to 14 respectively include one of Ethernet switches 51 to 54as a relay device for relaying communication with the other ECUs 15 to22. Furthermore, the ECUs 11 to 14 respectively have one ofmicrocomputers 61 to 64 as an arithmetic device. Although notillustrated, the microcomputers 61 to 64 respectively include a CPU, aROM, a RAM, and the like.

The switches 51 to 54 perform communication for relaying according tothe Ethernet standard. Each of the switches 51 to 54 includes four portsP1 to P4 for transmitting and receiving, and a communication controlunit 73 for performing various processes including a relay processaccording to the Ethernet standard. P1 and P2 are ring ports used forring network communication. P3 and P4 are normal ports. The number ofswitches is four in this example, but the number of switches may beother than four. Also, the number of ports is not limited to four, butmay be other than four. A communication control unit 73 is configuredby, for example, an integrated circuit or a microcomputer. Theoperations of the switches 51 to 54 are realized by the communicationcontrol unit 73.

In the in-vehicle communication network system 1, a port P1 of theswitch 51 of the ECU 11 and a port P1 of the switch 52 of the ECU 12 areconnected by a communication line 31. A port P2 of the switch 52 of theECU 12 and a port P1 of the switch 53 of the ECU 13 are connected by acommunication line 32. A port P2 of the switch 53 of the ECU 13 and aport P2 of the switch 54 of the ECU 14 are connected by a communicationline 33. A port P1 of the switch 54 of the ECU 14 and a port P2 of theswitch 51 of the ECU 11 are connected by a communication line 34.

In other words, the switches 51 to 54 are connected in a ring shape byconnecting the ring ports to one ring port of a first adjacent switch,an to one ring port of a second adjacent switch. Therefore, the switches51 to 54 and the communication lines 31 to 34 connecting the switches 51to 54 constitute a ring network capable of making frames go one round in(i.e., circulate through) the network.

The ECUs 15 and 16 are connected to ports P3 and P4 of the switch 51 ofthe ECU 11 via communication lines 35 and 36, respectively. The ECUs 17and 18 are connected to ports P3 and P4 of the switch 52 of the ECU 12via communication lines 37 and 38, respectively. The ECUs 19 and 20 areconnected to ports P3 and P4 of the switch 53 of the ECU 13 viacommunication lines 39 and 40, respectively. The ECUs 21 and 22 areconnected to ports P3 and P4 of the switch 54 of the ECU 14 viacommunication lines 41 and 42, respectively. That is, among the ports P1to P4 of the switches 51 to 54, the normal ports P3 and P4 (not used forthe ring network) are connected to the ECUs 15 to 22 as communicationterminals.

The communication paths between the switches 51 to 54 are, for example,two paths, i.e., (i) a counter-clockwise communication path in atransmission direction from the switch 51 to the switch 52, startingtransmission of frames from the switch 51, and (ii) a clockwisecommunication path in a transmission direction from the switch 51 to theswitch 54, starting transmission of frames from the switch 51. The twocommunication paths can function/serve as two communication paths forcommunication between the ECUs 15 to 22, which are connected todifferent switches 51 to 54. In other words, ECU 11 (including two ringports) may serve as a communications center for ECU 15 and ECU 16.

Hereinafter, the communication lines 31 to 34 connecting the switches 51to 54 may also be referred to as ring communication lines (or simplyring lines). Also, among the ports P1 to P4, the ports P1 and P2 usedfor the ring connection may also be referred to as ring ports. The portsother than the ring ports, that is, the ports P3 and P4 that are notused for the ring network may also be referred to as normal ports.

The frame communicated/transmitted in the in-vehicle communicationnetwork system 1 is, for example, an Ethernet frame shown in FIG. 2 .The Ethernet frame includes a preamble, a destination MAC (i.e., MediaAccess Control) address, a sender MAC address, a type, data, and FCS(i.e., Frame Check Sequence). The preamble may include the start offrame delimiter (SFD) marking the end of the preamble, to total 8 bytes.The destination MAC address is the MAC address of the destination deviceof the frame, and corresponds to a destination address. The sender MACaddress is a MAC address of a sender device of the frame, andcorresponds to a sender address.

Each of the switches 51 to 54 is provided with a respective memory 74.The memory 74 stores at least a MAC address table 75. The MAC addresstable 75 of each of the switches 51 to 54 registers, for each port inthe switch, the MAC addresses of the devices connected to the pathextending from the port. For example, in the MAC address table 75 of theswitch 51, a MAC address of the ECU 15 is registered for the normal portP3, and a MAC address of the ECU 16 is registered for the normal portP4. Further, MAC addresses of the ECUs 17 to 22 connected respectivelyto the normal ports P3 and P4 of the other switches 52 to 54 areregistered for the ring ports P1 and P2 of the switch 51. This isbecause the ECUs 17 to 22 are connected respectively to the ends of thepaths extending from the ring ports P1 and P2 of the switch 51 throughthe other switches 52 to 54. The registration of the MAC address in theMAC address table 75 is performed by, for example, a MAC addresslearning function of the respective switches 51 to 54.

Each of the switches 51 to 54 performs, for example, the followingprocess as a relay process in the Ethernet. When a frame is receivedfrom any of the ports P1 to P4, a subject switch, i.e., one of theswitches 51 to 54, determines a port to which the received frame istransferred (i.e., a transfer destination port), based on (i) thedestination MAC address in the received frame and (ii) the MAC addresstable 75. Then, the received frame is transmitted from the portdetermined as described above as a transfer destination port.

For example, assume that the ECU 15 has transmitted a frame addressed tothe ECU 19. The frame addressed to the ECU 19 is a frame including theMAC address of the ECU 19 as the destination MAC address. The frametransmitted from the ECU 15 includes the MAC address of the ECU 15 asthe sender MAC address. Here, a frame addressed to the ECU 19 andtransmitted from the ECU 15 is referred to as a frame f15-19.

In such case, the switch 51 receives the frame f15-19 from the port P3.When the switch 51 transmits the received frame f15-19 from the port P1among the two ports P1 and P2, the frame f15-19 is input to the port P1of the switch 53 via the switch 52, and is then transferred to the ECU19 from the port P3 of the switch 53.

Further, an ID (i.e., Identification) as identification information ofthe switch is stored in the memory 74 of the respective switches 51 to54. This ID is generated by random number processing, for example, andstored in the memory 74.

Further, a switch ID table 77 is also stored in the memory 74 of therespective switches 51 to 54. The switch ID table 77 of each of theswitches 51 to 54 is a table indicating (i) the IDs of the otherswitches connected in a ring shape and (ii) a connection order of theother switches viewed from at least one of the ring ports P1 and P2 ofthe switch. That is, the switch ID table 77 records the contents of theswitch of which ID is connected in which order as viewed from each ofthe ports P1 and P2 of the switch. The switch ID table 77 corresponds toconnection information. Note that how to generate the switch ID table 77is described later.

A switch ID table 77 of the switch 51 is illustrated in FIG. 3 , forexample. In addition, assuming that a code number assigned to a switchis “n” (i.e., 51 to 54), in FIG. 3 and the following description, an IDof the switch n is described as “IDn.”

As shown in FIG. 3 , in the switch ID table 77, for the respective ringports P1 and P2, the IDs of the other switches are registered in thesame order as the connection order of the other switches viewed from thering ports. Therefore, in the switch ID table 77 of the switch 51, forexample, the ID52 to ID54 of the other switches 52 to 54 are registeredin the order of “ID52→ID53→ID54” for the port P1 of the switch 51(counter-clockwise around the ring). For the port P2 of the switch 51,the ID52 to ID54 of the other switches 52 to 54 are registered in thestated order of “ID54→ID53→ID52” (clockwise around the ring).

In other words, the switch ID table 77 of each of the switches 51 to 54represents the connection order of the other switches viewedrespectively from the ring ports P1 and P2 by the order of IDregistration. In the example of FIG. 3 , the ID registered closer towardthe left side of the table 77 is an ID of the other switch closer to theport P1 or P2.

Note that the switch ID table 77 may be a table in which, for only oneof the two ring ports P1 and P2, the IDs of the other switches areregistered in the same order as the closeness of the switches connectedas viewed from the relevant ring port. In other words, the switch IDtable 77 may be a table having only one row (not shown), i.e., only anupper row or only a lower row of the table 77 shown in FIG. 3 . This isbecause, by reversing the order of the switches in one row, the order ofthe switches in the other row of the table 77 is known, in terms ofconnection order of the switches viewed from one of the two ring ports.In the switch ID table 77, the connection order of the switches may berepresented by adding a sequence number to each switch ID.

1-2. Function to Detect Abnormality of Ring Communication Line

The switches 51 to 54 have an abnormality detection function fordetecting an abnormal line from among the ring communication lines 31 to34.

In order to detect an abnormal ring communication line from among thelines 31 to 34, one of the switches 51 to 54 functions as a masterswitch, and the other switches function as slave switches. Here, it isassumed that the switch 51 is a master switch. Further, an abnormalitydetection frame and an abnormality notification frame, which aredescribed later, are frames transferred between the ring ports P1 and P2of the switches 51 to 54. In other words, those frames flow/circulate inthe ring-shape network.

The switch 51 as a master switch performs the following processes <1>,<2>, and <5>. The switches 52 to 54 respectively as slave switchesperform the following processes <3>, <4>, and <5>. Thus, processes <1>and <2> are performed only by the master switch. Processes <3> and <4>are performed only by the slave switches. And process <5> is performedby the master switch and by the slave switches.

<1> Process <1> is performed only by the master switch. The switch 51transmits an abnormality detection frame from one of the ring ports P1and P2 at regular time intervals Ti. Here, it is assumed that anabnormality detection frame is transmitted from the port P1. Theabnormality detection frame is, for example, a frame whose destinationMAC address is a code indicating that the frame is an abnormalitydetection frame.

Note that the abnormality detection frame transmitted from the port P1of the switch 51 circulates through, or goes around, the ring-shapenetwork to return to the port P2 of the switch 51 by the process <3>performed respectively by the switches 52 to 54, which is describedlater. In addition, the fixed/regular time interval Ti, which is atransmission interval of the abnormality detection frame, is longer thana time required for the abnormality detection frame to go around (i.e.,circulate through) the ring-shape network.

<2> Process <2> is performed only by the master switch. The masterswitch 51 determines whether any of (i) the abnormality detection frameand (ii) the abnormality notification frame has been received from theport P2 within a predetermined time T1 from the transmission of theabnormality detection frame. When neither of the abnormality detectionframe nor the abnormality notification frame is received within thepredetermined time T1, a master notification process described below isperformed.

Note that the predetermined time T1 is longer than the time required forthe abnormality detection frame to go around/circulate through thering-shape network to return to the switch 51. Further, in the switch51, a period/duration of the predetermined time T1 from the time oftransmission of the abnormality detection frame corresponds to aperiod/duration of time within which the abnormality detection frame orthe abnormality notification frame should be arriving at the switch 51.

<<Master Notification Process>>

The <<Master notification process>> is performed only by the masterswitch. The switch 51 identifies a switch that is connected first whenviewed from the port P2 from the ID table 77 of the switch 51 (i.e., theswitch 54). The switch is identified by identifying an ID of the switch.Then, for example, the switch 51 determines that an abnormality hasoccurred in the ring communication line 34 between the identified switchand the switch 51, then the switch 51 further notifies the otherswitches of such abnormal position by transmitting an abnormalitynotification frame including the ID of the switch 51 from the port P1.The abnormality notification frame is, for example, a frame whosedestination MAC address is a code indicating that the frame is anabnormality notification frame.

<3> Process <3> is performed only by the slave switches. When theabnormality detection frame is received from one of the ports P1 and P2,the slave switches 52 to 54 respectively transmit the receivedabnormality detection frame from the other one of the ports P1 and P2,i.e., from a port different than an upstream ring port from which theabnormality detection frame has been received.

<4> Process <4> is performed only by the slave switches. The slaveswitches 52 to 54 respectively determine whether any of (i) theabnormality detection frame and (ii) the abnormality notification frametransmitted by the other switch has been received from the upstream ringport among the ports P1 and P2 within a predetermined time T2 from areception of the abnormality detection frame. When it is determined thatneither the abnormality detection frame nor the abnormality notificationframe is received within the predetermined time T2, a slave notificationprocess described below is performed.

Note that the predetermined time T2 is longer than the fixed/regulartime Ti, which is the transmission interval of the abnormality detectionframe described above. Further, in the switches 52 to 54, a periodwithin the predetermined time T2 from the reception of the abnormalitydetection frame corresponds to a period within which the abnormalitydetection frame or the abnormality notification frame should be arrivingfrom the preceding switch.

<<Slave Notification Process>>

The <<Slave notification process>> is performed only by the slaveswitches. The switches 52 to 54 respectively identify a switch (i.e.,the preceding switch) that is connected first when viewed from theupstream ring port from the ID table 77 of the relevant switch. Then,the relevant switch determines that an abnormality has occurred in thering communication line(s) between the identified preceding switch(upstream switch) and the relevant switch, from among the ring lines 31to 34. Further, in order to notify the other switches of theabnormality, an abnormal notification frame including the ID of therelevant switch is transmitted (downstream) from one of the ports P1 andP2 which is different from the upstream ring port.

<5> Process <5> is performed by the master switch and by the slaveswitches. When the switches 51 to 54 respectively receive an abnormalitynotification frame transmitted by the other switch from one of the portsP1 and P2, the relevant switch transmits the received abnormalitynotification frame from a port different than the one that has receivedthe abnormality notification frame. Further, the switches 51 to 54respectively identify, from the ID table 77 of the relevant switch, aswitch further ahead of the switch whose ID is included in theabnormality notification frame just received. That is, a switch one stepfurther from the switch that has its ID included in the abnormalitynotification frame when viewed from one of the two ports P1, P2receiving such frame is identified, with reference to the ID table 77 ofthe relevant switch. Then, it is determined that an abnormality hasoccurred in the ring communication line between the identified switchand the switch having the ID included in the abnormality notificationframe from among the ring communication lines 31 to 34.

As described above, the switches 51 to 54 respectively use the switch IDtable 77 to identify one or more abnormal ring communication lines 31 to34, that is, an abnormal section of the ring-shape network. Further,each of the switches 51 to 54 has connection relation identifyinginformation that can identify which ECU is connected to the normal portof which switch. Then, each of the switches 51 to 54, when relaying aframe (hereinafter, referred to as a relay target frame) destinedfor/addressed to an ECU connected to the normal ports P3 and P4 of theother switches, performs a process described below, after identifyingthe abnormal section of the network.

Each of the switches 51 to 54 identifies, based on the connectionrelation identifying information, a destination switch of the relaytarget frame, i.e., a switch having the destination ECU connected to thenormal port thereof. Then, each of the switches 51 to 54 selects one ofthe ring ports P1 and P2 that can transmit a frame to the destinationswitch without passing through the abnormal section, based on the switchID table 77, and transmits the relay target frame from the selectedport. As described above, the switch ID table 77 is also used for aframe transfer that avoids an abnormal section.

1-3. Function to Generate Switch ID Table

Each of the switches 51 to 54 performs a table generating frametransmission process shown in FIG. 4 and a table generation processshown in FIG. 5 as a process for generating the switch ID table 77. Notethat the table generation process of FIG. 5 is performed as asubroutine, for example, in S250 of a first process of FIG. 6 describedbelow.

1-3-1. Table Generating Frame Transmission Process

The switches 51 to 54 perform the table generating frame transmissionprocess of FIG. 4 at regular intervals, for example. Then, in S100 ofthe table generating frame transmission process, the switches 51 to 54transmit a table generating frame from one of the ring ports P1 and P2of the relevant switch.

The table generating frame is, for example, a frame whose destinationMAC address is a code indicating that it is a table generating frame.The table generating frame circulates in the ring network, similarly tothe above-described abnormality detection frame and abnormalitynotification frame.

The ID of the sender switch is stored as the sender MAC address in thetable generating frame. The data area (i.e., payload) of the tablegenerating frame is used as an ID area for storing IDs of a plurality ofswitches. The ID area is empty at the time of transmission from thesender switch. The ID area corresponds to an area for storingidentification information.

Note that the switches 51 to 54 may be configured to transmit a tablegenerating frame from each/both of the ring ports P1 and P2.

1-3-2. Table Generation Process (when Table Generating Frame Received)

The switches 51 to 54 perform the table generation process shown in FIG.5 when a table generating frame is received from any of the ring portsP1 and P2. A switch presently receiving the table generating frame (andperforming the table generating process) may be called a subject switchor a receiving switch.

As shown in FIG. 5 , when one of the switches 51 to 54 starts the tablegeneration process (after receiving a table generating frame), in S120,the subject switch determines whether or not the received tablegenerating frame includes their subject ID. Specifically, it isdetermined whether or not the sender MAC address of the table generatingframe (the address of the switch that initiated/created/sent theabnormality detection frame) is the subject ID of the subject switch. Inother words, whether or not the sender MAC address of the tablegenerating frame is the ID of the receiving switch presently performingthe table generation process.

If the receiving switch determines in S120 that the sender MAC addressof the table generating frame is not its subject ID, then the receivingswitch determines that the sender of the received table generating frameis another switch, and the process proceeds to S130.

In S130, the subject switch inserts its subject ID at a head of an emptyarea in the ID area of the received table generating frame. Subsequentlyin the S140, the subject switch transmits the table generating framehaving the subject ID embedded therein from a ring port that isdifferent from the ring port that received the table generating frame.In other words, the table generating frame is transferred to the nextswitch in the ring. After that, the switches 51 to 54 end the tablegeneration process.

When the subject switch determines in S120 that the sender MAC addressof the table generating frame is its subject ID, the process proceeds toS150. In such case, the received table generating frame has gonearound/circulated through the entire ring network.

In S150, the subject switch generates the switch ID table 77 from (i.e.,based on) the IDs of the other switches embedded in the ID area of thereceived table generating frame and the arrangement sequence of each ID.

Specifically, the subject switch reads the IDs of the other switchesfrom the ID area of the received table generating frame in the order inwhich they were inserted. The IDs read from the ID area is collectivelycalled as an “ID group.” Then, the switches 51 to 54 perform thefollowing processes, i.e., first and second registration process.

<<First Registration Process>>

Of the ring ports P1 and P2, one that is different from the port thathas received the table generating frame, that is, the one thattransmitted the table generating frame, registers the read ID group asit is as the switch ID table 77. In otherwords, the ID group from atable generating frame sent from ring port P1 of switch 51 may readID52→ID53→ID54 for a counter-clockwise path, as shown in the upper halfof FIG. 3 .

<<Second Registration Process>>

Of the ring ports P1 and P2, one that has received the table generatingframe registers, as the switch ID table 77, the read ID group with areversely-ordered ID arrangement sequence. In other words, for ring portP2 of switch 51, we reverse the order of the ID group for a clockwisepath to read ID54→ID53→ID52, as shown in the bottom half of FIG. 3 .

For example, it is assumed that the switch 51 has transmitted a tablegenerating frame from the port P1 in S100 of FIG. 4 .

Then, the switch 52 receives the table generating frame transmitted bythe switch 51 from the port P1, and performs the process of S130 andS140 in FIG. 5 . Therefore, the switch 52 embeds the ID of the switch 52(i.e., the ID52) at the head of the empty area in the ID area of thereceived table generating frame, and transmits the table generatingframe having the ID52 embedded therein from the port P2 of the switch52.

The switch 53 receives the table generating frame transferred from theswitch 52 from the port P1, and performs the process of S130 and S140 inFIG. 5 . Therefore, the switch 53 transmits, from the port P2, the tablegenerating frame in which the ID of the switch 53 (i.e., the ID53) isadded to the ID area. For example, ID53 is added immediately after theID52).

The switch 54 receives the table generating frame transferred from theswitch 53 from the port P2, and performs the process of S130 and S140 inFIG. 5 . Therefore, the switch 54 transmits the table generating framein which the ID of the switch 54 (i.e., the ID54) is added to the IDarea from the port P1.

Then, the switch 51 receives the table generating frame transferred fromthe switch 54 from the port P2, which has the sender MAC address of thesubject switch, i.e., the ID of the switch 51 (i.e., the ID51).

Therefore, the switch 51 generates the switch ID table 77 shown in FIG.3 by performing the process of S150 shown in FIG. 3 . In other words,for the port P1, the ID52 to ID54 of the other switches 52 to 54 areregistered in the order of “ID52→ID53→ID54” by the above-described firstregistration process. For the port P2, the ID52 to ID54 are registeredin the order of “ID54→ID53→ID52” by the above-described secondregistration process.

Similarly, the other switches 52 to 54 generate the switch ID table 77by performing the process of FIG. 4 (each creating a respective tablegenerating frame) and the process of S150 of FIG. 5 (each creating arespective switch ID table for itself).

1-4. Processes for Correcting Switch ID Table when ID is Duplicated

The switches 51 to 54 may, for some reason such as process error ornoise, store the subject ID (i.e., an ID assigned to one switch) also asan ID of an other switch. In other words, ID duplication may occur. WhenID duplication occurs, in a switch having no ID duplication, the same IDmay be registered as an ID of a first switch and also as an ID ofanother switch in the switch ID table. For example, in FIG. 4 the switchID table for ring port P1 of switch 51 may be: ID52→ID52→ID54 (insteadof ID52→D53→ID54). Further, in a switch having ID duplication, thesender of the table generating frame cannot be identified, thereby thegeneration of the switch ID table itself may not be performed properly.For example, in FIG. 4 the switch ID table for ring port P1 of switch 51may be: ID51→ID53→ID54 (instead of ID52→ID53→ID54). When ID duplicationoccurs as described above, the switch ID table may not be correct in theswitches 51 to 54, and a correct result cannot be obtained as a resultof the process that uses the switch ID table. For example, an abnormalsection of the network cannot be properly identified, or frame transferthat avoids the abnormal section cannot be properly performed.

Therefore, in the present embodiment, in order to eliminate IDduplication and correct the switch ID table when ID duplication occurs,each of the switches 51 to 54 performs the first process to the fourthprocess shown in FIGS. 6 to 9 .

1-4-1. First Process (Anti-Duplication)

The switches 51 to 54 each perform the first process shown in FIG. 6when receiving the above-described table generating frame.

In FIG. 6 , when the switches 51 to 54 start the first process, in S210,the switches 51 to 54 determine whether or not the sender MAC address ofthe received table generating frame is their subject ID (i.e., an ID ofthe receiving/subject switch). If it is determined that the sender MACaddress is the subject ID, the process proceeds to S220. For example,switch 51 receives a table generating frame, then determines in stepS210 that the sender MAC address is ID51 (“YES”), then proceedsrightward and downward to step S220.

Continuing the example, in S220 switch 51 determine whether or not theID area (i.e., the payload) of the received table generating frame isempty. If the ID area is not empty, the process proceeds to S230. Here,“empty” means that no switch ID is stored. This indicates an error,because a table generating frame in this situation (initially generatedby the switch that is now receiving) should have at least one ID in theID area.

Additionally switch 51 also proceeds to S230 after determining in S210that the sender MAC address of the received table generating frame isnot ID51. In S230, switch 51 determines whether or not the same ID asthe subject ID is stored in the ID area of the received table generatingframe. If it is determined that the same ID is not stored, the processproceeds to S240 based on a determination of no ID duplication. Here,“no ID duplication” means that no ID duplication has occurred.

In step S240, switch 51 permits transmission of the table generatingframe in S240. If the transmission of the table generating frame waspreviously prohibited by other process described later, then thetransmission of the table generating frame is restarted/resumed with thepermission in S240.

Then, subsequently in the S250, the switch 51 performs theabove-described table generation process of FIG. 5 , and subsequentlyends the first process.

Further, when switch 51 determines in S220 that the ID area of thereceived table generating frame is empty, the switch 51 determines thatID duplication has occurred, and the process proceeds to S260. In suchcase, ID duplication would have occurred between the two adjacentswitches, i.e., (i) the switch receiving the table generating frame and(ii) an adjacent switch connected to one of the ports P1 and P2 of theswitch receiving the table generating frame (hereinafter referred to asan upstream adjacent switch). For example, in counter-clockwise rotationin FIG. 1 , switch 54 and switch 51 have the same ID. This is a type 1duplication error (or “upstream adjacent switch” error).

Note, there is another possible type of error here, which is that allintervening switches (52-54 in FIG. 1 ) omitted inserting their IDs intothe data generating frame. Yet another possible type of error is that P1of switch 51 is directly connected to P2 of switch 51, such that thereis only one switch connected to itself. It is not clear whether thissingle self-connected switch is qualifies as a ring network, perhaps asa degenerate ring network. Note that Ethernet defines 3 as the minimumnumber of switches in an Ethernet ring network.

Further, the switches 51 to 54 also determine that ID duplication hasoccurred when it is determined in S230 that the same ID as the subjectID (i.e., the ID of the subject switch) is stored in the ID area of thereceived table generating frame, the process proceeds to S260. In suchcase, it is considered that the ID is duplicated between any of theswitches other than the upstream adjacent switch and the subject switch.This is a type 2 duplication error, which is mutually exclusive withrespect to type 1 duplication errors.

In other words, the processes of S210 to S230 in FIG. 6 are processesfor determining the presence/absence of ID duplication. It may also bedescribed as a process for determining whether or not a switch havingthe same ID as the subject switch is present in the in-vehiclecommunication network system 1. Then, among the switches 51 to 54, theswitch that has determined that ID duplication has occurred by theprocess of S210 to S230 is a switch that has detected ID duplication. Itshould be noted that presence or absence of ID duplication may bedetermined by only one of the determination in S230 and thedeterminations in S210 and S220. In other words, it is possible to onlysearch for one type of duplication error.

The switches 51 to 54 prohibit the transmission of the table generatingframe in S260. Specifically, the switches 51 to 54 prohibit the tablegenerating frame transmission process of FIG. 4 . Then, the switches 51to 54 initialize (i.e., delete) the switch ID table stored in the switchin S270, and re-generate their subject ID subsequently in S280. Forexample, in S280, a new subject ID is generated by random numberprocessing, and the generated new subject ID is stored in the memory 74.

Subsequently in S290, the switches 51 to 54 transmit a duplicationnotification frame for notifying the other switches that ID duplicationhas occurred from at least one of the ring ports P1 and P2 of theswitch, and end the first process.

The duplication notification frame is, for example, a frame in which thedestination MAC address is a code indicating that it is a duplicationnotification frame. The duplication notification frame is also a frameflowing/circulating through the ring-shape network, similarly to theabnormality detection frame and the abnormality notification framedescribed above. Further, in the duplication notification frame, the newID generated in S280 is stored as the ID of the sender switch. Forexample, the re-generated ID may be stored as the sender MAC address ofthe duplication notification frame, or may be stored in the data area ofthe duplication notification frame. Note that, in S290, the switches 51to 54 may transmit the duplication notification frame from the ring portP1 or P2 which is different from the one from which the table generatingframe was received, or may transmit the duplication notification framefrom the port receiving the table generating frame. Further, theduplication notification frame may be transmitted from both of the ringports P1 and P2.

In addition, when the switches 51 to 54 re-generate their subject ID inS280 in FIG. 6 and subsequently perform the process in S130 in FIG. 5 ,the switches 51 to 54 write (or insert) the re-generated new subject IDat the head of the empty area in the ID area of the received tablegenerating frame.

1-4-2. Second Process

The switches 51 to 54 perform the second process shown in FIG. 7 atpredetermined intervals.

In FIG. 7 , when the switches 51 to 54 start the second process, inS310, the switches 51 to 54 determine whether or not a duplicationnotification frame including the subject ID has been received from oneof the ring ports P1 and P2. If the duplication notification frameincluding the subject ID has not been received, the process proceeds toS320. Then, in S320, the switches 51 to 54 transmit the same frame asthe duplication notification frame transmitted in S290 of FIG. 6 fromone of the ring ports P1 and P2, and subsequently end the secondprocess. When the switches 51 to 54 determine in S310 that theduplication notification frame including the subject ID has beenreceived, the switch 51 to 54 end the second process.

In other words, the switches 51 to 54 transmit the same duplicationnotification frame including the new subject ID re-generated in S280 ofFIG. 6 at regular intervals, until the duplication notification frametransmitted from the subject switch goes around/circulates through thenetwork and returns to the subject switch. For example, SW 51 receivedanew ID as SW 91 (ID91) during step S280 in FIG. 6 . The duplicationnotification frame (with ID91 as the sender MAC address) passes fromaround the ring network until it reaches SW 91 (previously SW 51), thenin step S310 of FIG. 7 the sender MAC address is the same as the subjectaddress, then step S320 (transmittal) is skipped (not performed), thenthe duplication notification frame stops being transmitted.

Note that the switches 51 to 54 may transmit the duplicationnotification frame in S320 either (i) from the same one of the ringports P1 and P2 that has transmitted the frame in S290 in FIG. 6 , or(ii) from a different one of the ring ports P1 and P2 that hastransmitted the frame in S290 in FIG. 6 . Also, in S320, the duplicationnotification frame may be transmitted from both of the ring ports P1 andP2.

1-4-3. Third Process

The switches 51 to 54 perform the third process shown in FIG. 8 whenreceiving the duplication notification frame from any of the ring portsP1 and P2.

As shown in FIG. 8 , when the switches 51 to 54 start the third process,in S410, the switches 51 to 54 determine whether or not the ID includedin the received duplication notification frame is their subject ID, andif the ID in the duplication notification frame is the subject ID, theprocess proceeds to S420. That is, the process proceeds to S420 when theduplication notification frame transmitted from the sender has returnedto the sender after going around/circulating through the network.

In S420, the switches 51 to 54 stop transmission of the duplicationnotification frame. Specifically, the switches 51 to 54 stop performingthe second process shown in FIG. 7 . Subsequently in S430, the switches51 to 54 transmit the table generating frame from at least one of thering ports P1 and P2 by performing the same process as in S100 of FIG. 4. In the table generating frame transmitted in S430, the new subject IDgenerated in S280 in FIG. 6 is stored as the sender MAC address. Then,the switches 51 to 54 end the third process after transmitting the tablegenerating frame in S430. Note that in S430, the switches 51 to 54 maypermit to perform the process in FIG. 4 , which has been prohibited inS260 in FIG. 6 . Further, a table generating frame storing a new subjectID as a sender MAC address may be transmitted by permitting to performthe process of FIG. 4 in S430.

When the switches 51 to 54 determine in S410 that the ID included in thereceived duplication notification frame is not their subject ID, thatis, when receiving a duplication notification frame from a senderdifferent from the subject switch, the process proceeds to S440.

In S440, the switches 51 to 54 prohibit the transmission of the tablegenerating frame from the relevant switch. Specifically, the switches 51to 54 prohibit performing the table generating frame transmissionprocess in FIG. 4 .

Then, subsequently in S450, the switches 51 to 54 transmit the receivedduplication notification frame from one of the ring port P1 or P2 whichis different from the receiving port that has received the duplicationnotification frame. In other words, the duplication notification framefrom the other switch is transferred to the next switch. Then, theswitches 51 to 54 end the third process.

1-4-4. Fourth Process, FIG. 9

When the switches 51 to 54 prohibit the transmission of the tablegenerating frame from the relevant switch in S440 of FIG. 8 due to thereception of the duplication notification frame having the other switchas a sender, the switches 51 to 54 perform the fourth process shown inFIG. 9 .

In FIG. 9 , when the switches 51 to 54 start the fourth process, inS510, the switches 51 to 54 determine whether or not the relevant switchhas received the duplication notification frame of having the otherswitch as a sender within a predetermined time Ts1 after starting thefourth process. When the duplication notification frame is receivedwithin the predetermined time Ts1, the fourth process ends. Note thatthe predetermined time Ts1 is set to be longer than a cycle in which thesecond process of FIG. 7 is performed, that is, a cycle in which theswitch that has detected the ID duplication repeatedly transmits theduplication notification frame.

If the switches 51 to 54 determine in S510 that the relevant switch hasnot received the duplication notification frame having the other switchas a sender within the predetermined time Ts1, the process proceeds toS520 and permits transmitting the table generating frame from therelevant switch. Specifically, the switches 51 to 54 permit performingthe table generating frame transmission process in FIG. 4 . With thepermission in S520, the transmission of the table generating frame isrestarted/resumed. Then, the switches 51 to 54 end the fourth process.

In such manner, when the switches 51 to 54 receive the duplicationnotification frame from the other switch and prohibit the transmissionof the table generating frame from the relevant switch, the switches 51to 54 restart/resume the transmission of the table generating frame fromthe relevant switch in two cases. The first case is a case where a tablegenerating frame is received from the other switch and the process ofS240 in FIG. 6 is performed. The second case is a case where the processof S520 in FIG. 9 is performed after receiving no duplicationnotification frame from the other switch for the predetermined time Ts1or more.

1-5. Example of Operation

For a first example, it is assumed that the IDs stored in the switches52 and 54 have been somehow duplicated. For example, switches 52 and 54both store ID52 in their respective memory 74. Then, in a state wheresuch ID duplication has occurred, for example, the switch 51 transmits atable generating frame from the port P1.

The table generating frame transmitted from the switch 51 is transmittedcounterclockwise through the ring-shape network and reaches the port P2of the switch 54 via the switches 52 and 53. When the switch 54 receivesthe table generating frame having the switch 51 as a sender, the switch54 performs the first process of FIG. 6 , determines “NO” in S210, anddetermines “YES” in S230, thereby detecting ID duplication. This isbecause the same ID as that of the switch 54 is stored by the switch 52in the ID area of the table generating frame transmitted from the switch51 to the switch 54. As a second example, assuming that ID duplicationoccurs between the switch 53 and the switch 54 and the switch 53transmits a table generating frame from the port P2, the switch 54determines “YES” in S210 and S220 in FIG. 6 , thereby detecting IDduplication. Specifically, this second example is an “immediatelyadjacent duplication error” (type 1 error), and is different that theerror in the first example (type 2 error).

Then, the switch 54 that has detected ID duplication performs theprocesses S260 to S290 in FIG. 6 . Therefore, the switch 54 prohibitstransmission of the table generating frame from the switch 54,initializes the switch ID table, and generates a new subject ID (such asID54new, preferably different than the previous ID54, although there isa small chance that a random number generator may generate an identicalID, this possibility may result in additional generations until anew IDis generated). Then, in order to notify other switches 51 to 53 of theoccurrence of ID duplication, a duplication notification frame includingthe new subject ID is transmitted from at least one of the ring ports P1and P2 of the switch 54 (ID54new). In this example, it is assumed that aduplication notification frame is transmitted from the port P1 of theswitch 54.

Then, the switch 51 receives the duplication notification frame havingthe switch 54 (ID54new) as a sender from the port P2, performs the thirdprocess of FIG. 8 , determines “NO” in S410, and performs the process ofS440 and S450. Therefore, the switch 51 prohibits the transmission ofthe table generating frame from the switch 51. Then, the receivedduplication notification frame is transferred from the port P1 to thenext switch 52.

The switch 52 receives the duplication notification frame transmitted bythe switch 54 as a sender (i.e., originated from the switch 54) from theport P1, performs the third process of FIG. 8 , determines “NO” in S410,and performs the process of S440 and S450. Therefore, the switch 52 alsoprohibits transmission of the table generating frame from the switch 52.Then, the received duplication notification frame is transferred fromthe port P2 to the next switch 53.

The switch 53 receives the duplication notification frame transmitted bythe switch 54 as a sender from the port P1, performs the third processin FIG. 8 , determines “NO” in S410, and performs the process of S440and S450. Therefore, the switch 53 also prohibits transmission of thetable generating frame from the switch 53. Then, the receivedduplication notification frame is transferred from the port P2 to thenext switch 54.

Then, the switch 54 receives the duplication notification frameincluding the re-generated new subject ID (ID54new) and having theswitch 54 as a sender from the port P2, and performs the third processof FIG. 8 . Then, the switch 54 determines “YES” in S410 of FIG. 8 andperforms the process of S420 and S430. Therefore, the switch 54 (afterthe duplication notification frame completes transmission through thewhole ring, and returns to the creator/originator of the duplicationnotification frame) stops transmission of the duplication notificationframe, and transmits a table generating frame including the re-generatednew subject ID as a sender MAC address from at least one of the ringports P1 and P2.

On the other hand, in case that the other switches 51 to 53 receive thetable generating frame having the switch 54 as a sender when thetransmission of the table generating frame is prohibited in accordancewith the reception of the duplication notification frame, the otherswitches 51 to 53 perform the first switch of FIG. 6 . Then, the processof S240 and S250 is performed by determining “NO” in S210 and S230 ofFIG. 6 .

Therefore, the switches 51 to 53 permit and restart/resume thetransmission of the table generating frame, and perform the tablegeneration process of FIG. 5 . In such case, the switches 51 to 53determine “NO” in S120 of FIG. 5 and perform the process of S130 andS140.

Therefore, the table generating frame transmitted by the switch 54returns to the switch 54 after a round trip of the ring network, by theprocess of S130 and S140 in FIG. 5 performed by the switches 51 to 53.Then, the switch 54 generates the switch ID table from the ID groupstored in the ID area of the table generating frame coming back from theround trip of the network.

Further, each of the other switches 51 to 53 also transmits the tablegenerating frame, and re-generates the switch ID table from the ID groupstored in the ID area of the table generating frame returned from theround trip of the ring network.

Here, when the switch 54 receives the table generating frame having theother switches 51 to 53 as a sender and performs the process of S130 inFIG. 5 , the switch 54 writes, in the ID area of the received tablegenerating frame, the generated new subject ID (ID54new). Therefore, inthe switch ID tables generated by the other switches 51 to 53, an IDdifferent from the ID of the switch 52 is recorded as the ID of theswitch 54. Therefore, the switch ID tables of the switches 51 to 54 arecorrected and thus have no ID duplication.

1-6. Effect

According to the first embodiment described in detail above, thefollowing effects are obtained. (1a) When the switches 51 to 54 detectthe ID duplication by the process of S210 to S230 in FIG. 6 , that is,when it is determined that a switch having the same ID as that of theother switch exists in the in-vehicle communication network system 1, anew subject ID (such as ID54new) is generated in S280 of FIG. 6 . Inother words, a subject switch detecting ID duplication (with respect toits own ID) changes its subject ID, thereby eliminating ID duplication.Then, the subject switch subsequently transmits the table generatingframe including the re-generated new subject ID from at least one of theports P1 and P2 in S430 of FIG. 8 .

The table generating frame from the subject switch that has detected theID duplication goes around the ring network while recording the ID ofeach of the other switches recorded respectively by the other switch,and returns to the subject switch that has detected the ID duplication.Then, the subject switch that has detected the ID duplication generatesa new switch ID table and stores it in the memory 74 by the process ofS150 in FIG. 5 .

Further, when the subject switch that has detected the ID duplicationreceives the table generating frame having the other switch as a senderafter generating its new subject ID (such as ID54new), the switch embedsthe re-generated new subject ID in the ID area of the table generatingframe in S130 of FIG. 5 . Therefore, in the other switch that is thesender of the table generating frame, a switch ID table in which thegenerated new ID is recorded as an ID of the ID duplication detectedswitch is generated and stored in the memory 74.

Therefore, even if ID duplication occurs, a switch ID table in which IDduplication has been eliminated is generated and stored in each of theswitches 51 to 54. In other words, the switch ID table stored/held ineach of the switches 51 to 54 is correctable.

(1b) When detecting the ID duplication, the switches 51 to 54 transmitthe duplication notification frame including the re-generated newsubject ID in S290 of FIG. 6 before transmitting the table generatingframe, from at least one of the ring ports P1 and P2. Subsequently, whena duplication notification frame including the new subject ID isreceived from any of the ring ports P1 and P2, the table generatingframe is transmitted in S430 of FIG. 8 .

Further, when the switches 51 to 54 receive the duplication notificationframe having the other switch as a sender from one of the ring ports P1and P2, the switches 51 to 54 prohibit the transmission of the tablegenerating frame in S440 of FIG. 8 . Then, in S450 of FIG. 8 , thereceived duplication notification frame is transmitted from one of thering ports P1 and P2 that is different from the receiving port that hasreceived the duplication notification frame. Subsequently, transmissionof the table generating frame from the switch is restarted/resumed oncondition that the table generating frame is received. The transmissionrestart is realized by the process of S240 in FIG. 6 .

Therefore, among the switches 51 to 54, the subject switch that hasdetected the ID duplication enables the other switches to prohibit thetransmission of the table generating frame by the duplicationnotification frame, and to transmit the table generating frametherefrom. Then, the subject switch detecting the ID duplicationtransmitting the table generating frame, causes the other switches toresume transmission of the table generating frame.

Therefore, among the switches 51 to 54, the switch that has detected theID duplication and has re-generated its subject ID is enabled totransmit the table generating frame first, and then makes the otherswitches transmit the table generating frame. In other words, when anyof the switches 51 to 54 detects the ID duplication, the switch that hasdetected the ID duplication first transmits a table generating frame forre-generating a switch ID table having no ID duplication. Then, inswitches other than the switch that has detected the ID duplication, thereception of the duplication notification frame is used as a trigger torecognize that, during a period from the reception of the duplicationnotification frame to the re-generation of the switch ID table, theswitch ID table is not stored/held as a correct one. Therefore, duringsuch period, for example, by stopping the process using the switch IDtable, it is possible to suppress an inappropriate process result frombeing obtained.

(1c) Among the switches 51 to 54, a switch that has detected the IDduplication transmits the duplication notification frame in S290 of FIG.6 and subsequently transmits, or keeps transmitting, the sameduplication notification frame in S320 of FIG. 7 at regular intervalsuntil receiving the duplication notification frame transmitted by thesubject switch. Therefore, the reachability of the duplicationnotification frame to the other switches can be increased.

(1d) When the switches other than the switch that has detected the IDduplication among the switches 51 to 54 have prohibited the transmissionof the table generating frame by receiving the duplication notificationframe, those switches restart/resume transmission of the tablegenerating frame also when determining “NO” in S510 of FIG. 9 . Inotherwords, the transmission of the table generating frame isrestartable/resumable based not only on a satisfaction of a conditionthat “the table generating frame is received from the other switch” butalso on a satisfaction of condition that “the duplication notificationframe has not been received for the predetermined time Ts1 or more.”Therefore, a situation in which transmission of the table generatingframe is kept/left prohibited is preventable.

In the first embodiment, the table generating frame corresponds to thegenerating frame. The memory 74 corresponds to a storage unit. S100 inFIG. 4 corresponds to the process as a generating frame transmitter.Steps S130 and S140 in FIG. 5 correspond to process as a transferprocessing unit. S150 in FIG. 5 corresponds to the process as agenerating unit. S210 to S230 in FIG. 6 correspond to the process as aduplication determination unit. S280 and S290 in FIG. 6 , steps S310 andS320 in FIG. 7 , and S430 in FIG. 8 correspond to the process as aduplication elimination unit and a first duplication elimination unit.S440 and S450 in FIG. 8 , S240 in FIG. 6 , and S520 in FIG. 9 correspondto the process as a second duplication elimination unit.

2. Second Embodiment, FIGS. 10-13 2-1. Differences from First Embodiment

Since a basic configuration of the second embodiment is the same as thatof the first embodiment, differences are described below. The samereference numerals as in the first embodiment denote the samecomponents, and reference is made to the preceding description.

The in-vehicle communication network system 1 according to the secondembodiment is different from the first embodiment in that the switches51 to 54 further perform fifth to eighth processes shown in FIGS. 10 to13 .

2-2. Fifth to Eighth Processes

The fifth to eighth processes in FIGS. 10 to 13 correspond to a casewhere one of the switches 51 to 54 is reset, the ID and the switch IDtable 77 in the memory 74 thereof are lost (for example, temporarilylosing power when the memory is “volatile” memory that requirescontinuous power to maintain stored information, or alternatively byclearing a “non-volatile” memory during a reset process), and then therelevant switch is restarted. Each of the above processes involves aprocess for correcting the switch ID table in each of the switches 51 to54.

2-2-1. Fifth Process

When started/re-started, the switches 51 to 54 perform a fifth processshown in FIG. 10 . As shown in FIG. 10 , when the switches 51 to 54start the fifth process, in S610, the switches 51 to 54 determinewhether or not they have been restarted from a reset. Specifically, itis determined whether the subject switch has been restarted after areset in a state where the subject switch is a component of thein-vehicle communication network system 1 and the switch ID table hasalready been generated together with the other switches (i.e., theswitch ID table has already been generated in all of the switches in thenetwork system 1).

For example, in S610, it is determined whether or not theabove-described abnormality notification frame has been received withina predetermined time after starting, and if the abnormality notificationframe has been received, it may be determined that the system 1 has beenrestarted from a reset. The above determination is reasonable because,in the in-vehicle communication network system 1, when one of theswitches 51 to 54 is reset, the reset switch (i.e., a switch beingreset) becomes incapable of transmitting/receiving frames, which causesone of the other switches to determine the situation as a ringcommunication line abnormality and to transmit the abnormalitynotification frame. Also, for example, when the switch ID table isgenerated during operation, the switches 51 to 54 store a generationhistory indicating the table generation operation when a switch ID tableis generated, in a storage such as a rewritable non-volatile memory or apower-backed RAM, etc., i.e., in an operation history memory that doesnot lose memory contents by a reset. Then, in S610, the switches 51 to54 determine whether or not a generation history is stored in theoperation history memory. If a generation history is stored therein, theswitches 51 to 54 determine that restart has been performed from areset, and the generation history may be deleted subsequently.

If the switches 51 to 54 do not determine in S610 that they haverestarted from a reset, the switches 51 to 54 end the fifth process.However, if the switches 51 to 54 determine that they have restartedfrom a reset, the process proceeds to S620.

In S620, the switches 51 to 54 generate a new subject ID by randomnumber processing, for example, and store the generated new subject IDin the memory 74. Optionally, the subject switch may determine/verifythat the new subject ID is different from the old subject ID. Then,subsequently in S630, the switches 51 to 54 transmit an initializationframe for notifying other switches of an initialization and a (new)generation of the switch ID table from at least one of the ring ports P1and P2 of the switch, and end the fifth process subsequently.

The initialization frame may be, for example, a frame whose destinationMAC address is a code indicating that the frame is an initializationframe. The initialization frame is also a frame flowing through thering-shape network, just like the abnormality detection frame and theabnormality notification frame described above. In the initializationframe, the new ID generated in S620 is stored as the ID of the senderswitch. For example, the new ID may be stored as the sender MAC addressof the initialization frame, or may be stored in the data area of theinitialization frame, or stored in both locations. Note that theswitches 51 to 54 may transmit the initialization frame from one of thering port P1 or P2 which is different from the port that has receivedthe abnormality notification frame in S630, or the abnormalitynotification frame may be transmitted from one of the ring port P1 or P2from the port that has received the abnormality notification frame.Further, the initialization frame may be transmitted from both of thering ports P1 and P2.

Further, when performing the process of S130 of FIG. 5 afterre-generating the subject IDs in S620 of FIG. 10 , the switches 51 to 54embed the re-generated new subject ID at the head of the empty area ofthe ID area of the received table generating frame.

2-2-2. Sixth Process, FIG. 11

When transmitting the initialization frame in S630 of FIG. 10 , theswitches 51 to 54 perform a sixth process shown in FIG. 11 atpredetermined intervals.

As shown in FIG. 11 , when the switches 51 to 54 start the sixthprocess, the switches 51 to 54 determine in S710 whether or not aninitialization frame including their subject ID has been received fromone of the ring ports P1 and P2. If an initialization frame includingthe subject ID has not been received, the process proceeds to S720.

Then, in S720, the switches 51 to 54 transmit the same frame as theinitialization frame transmitted in S630 of FIG. 10 from one of the ringports P1 and P2, and subsequently end the sixth process. Alternatively,when the switches 51 to 54 determine in S710 that the initializationframe including the subject ID has been received, the switch 51 to 54end the sixth process.

In other words, the switches 51 to 54 repeatedly transmit theinitialization frame (i) including the new subject ID re-generated inS620 of FIG. 10 and (ii) indicating the relevant switch as a sender atregular intervals until such an initialization frame returns to thesender switch after making a round trip of the network.

Note that, in S720, the switches 51 to 54 may transmit theinitialization frame from one of the ring port P1 or P2 which is thesame as the port transmitted in S630 of FIG. 10 , or may transmit theinitialization frame in S630 of FIG. 10 from a port different therefrom.Further, in S720, the initialization frame may be transmitted from bothof the ring ports P1 and P2.

2-2-3. Seventh Process, FIG. 12

The switches 51 to 54 perform a seventh process shown in FIG. 12 whenreceiving the initialization frame from one of the ring ports P1 and P2.

In FIG. 12 , when the switches 51 to 54 start the seventh process, inS810, the switches 51 to 54 determine whether or not an ID included inthe received initialization frame is their subject ID. If an ID in thereceived frame is the subject ID of the relevant switch, the processproceeds to S820. That is, when the switches 51 to 54 receive aninitialization frame having the relevant switch as a sender after around trip of the network, the process proceeds to S820.

In S820, the switches 51 to 54 stop transmission of the initializationframe. Specifically, the sixth process shown in FIG. 11 is stopped.Subsequently in S830, the switches 51 to 54 transmit the tablegenerating frame from at least one of the ring ports P1 and P2 byperforming the same process as shown in S100 in FIG. 4 . In the tablegenerating frame transmitted in S830, the new subject ID re-generated inS620 of FIG. 10 is stored as the sender MAC address. After transmittingthe table generating frame in S830, the switches 51 to 54 end theseventh process. Note that, in S830, by starting the process in FIG. 4 ,for example, a table generating frame in which a new subject ID isstored as the sender MAC address may be transmitted.

Further, when the switches 51 to 54 determine in above-described S810that an ID included in the received initialization frame is not theirsubject ID, that is, when the received initialization frame is a framefrom one of the other switches, the process proceeds to S840.

In S840, the switches 51 to 54 initialize (i.e., delete) the switch IDtable stored in the switch, and generate their new subject IDsubsequently in S850. For example, in S850, a new subject ID isgenerated by random number processing, and the generated new subject IDis stored again in the memory 74.

Then, subsequently in S860, the switches 51 to 54 prohibit thetransmission of the specific frame from the relevant switch. Thespecific frame includes a table generating frame, at least. Furthermore,the specific frame may also include, for example, an abnormalitydetection frame and an abnormality notification frame.

Then, subsequently in S870, the switches 51 to 54 transmit the receivedinitialization frame from one of the ring port P1 or P2 which isdifferent from the port that has received the initialization frame. Inother words, the initialization frame from the other switch istransferred to the next switch. Subsequently, the switches 51 to 53 endthe seventh process.

2-2-4. Eighth Process, FIG. 13

When the switches 51 to 54 has prohibited the transmission of the tablegenerating frame from the relevant switch in S860 in FIG. 12 due to thereception of the initialization frame from a sender other than therelevant switch, the switches 51 to 54 perform an eighth process shownin FIG. 13 at predetermined intervals.

After starting the eighth process, as shown in FIG. 13 , the switches 51to 54 in S910 respectively determine whether or not an initializationframe from an other sender, i.e., a switch other than therelevant/subject switch, has been received within a predetermined timeTs2. When it is determined that the initialization frame has beenreceived within the predetermined time Ts2, the switches 51 to 54 endthe eighth process. Note that the predetermined time Ts2 is set to atime longer than a cycle in which the sixth process in FIG. 11 isperformed, that is, a cycle in which the switch restarted from a resetrepeatedly transmits the initialization frame.

When the switches 51 to 54 respectively determine in S910 that theinitialization frame from the other sender has not been received withinthe predetermined time Ts2, the process proceeds to S920 to permit thetransmission of a table generating frame from the relevant switch. Withthe permission in S920, the transmission of the table generating framefrom the relevant switch is restarted. After that, the switches 51 to 54end the eighth process. Note that, when the transmission of theabnormality detection frame and the abnormality notification frame isprohibited in S860 in FIG. 12 , the transmission of these frames ispermitted, for example, after the switch ID table is re-generated in therelevant switch.

Therefore, after receiving the initialization frame from the otherswitch and prohibiting the transmission of the table generating framefrom the relevant switch, the switches 51 to 54 respectively restart thetransmission of the table generating frame from the relevant switch inthe third case or in the fourth case. (Recall that the first case andthe second case were previously discussed above regarding the fourthprocess and FIG. 9 .)

The third case is a case where a table generating frame is received fromthe other switch and the process of S240 in FIG. 6 is performed. Thefourth case is a case where the process of S920 of FIG. 13 is performedafter receiving no initialization frame from the other switch for thepredetermined time Ts2 or more.

2-3. Operation Example

For example, it is assumed that the switch 54 among the switches 51 to54 is reset and restarted.

The switch 54 is restarted (after a reset) and performs the fifthprocess of FIG. 10 . Then, “YES” is determined in S610 of FIG. 10 , andthe process of S620 and S630 is performed. Therefore, the switch 54generates its (new) subject ID. Then, in order to cause the otherswitches 51 to 53 to initialize and generate the (new) switch ID table,an initialization frame including the new subject ID is transmitted fromat least one of the ring ports P1 and P2. In this example, it is assumedthat an initialization frame is transmitted from the port P1 of theswitch 54.

Then, the switch 51 receives the initialization frame transmitted by theswitch 54 from the port P2, performs the seventh process of FIG. 12 ,determines “NO” in S810, and performs the processes of S840 to S870.Therefore, the switch 51 initializes the switch ID table, generates itsnew subject ID, and prohibits transmission of the table generating framefrom the switch 51. Then, the received initialization frame istransferred from the port P1 to the next switch 52.

The switch 52 receives the initialization frame transmitted by theswitch 54 from the port P1, performs the seventh process of FIG. 12 ,determines “NO” in S810, and performs the processes of S840 to S870.Therefore, the switch 52 also initializes the switch ID table,re-generates its subject ID, and prohibits transmission of the tablegenerating frame from the switch 52. Then, the received initializationframe is transferred from the port P2 to the next switch 53.

The switch 53 receives the initialization frame transmitted by theswitch 54 from the port P1, performs the seventh process of FIG. 12 ,determines “NO” in S810, and performs the processes of S840 to S870.Therefore, the switch 53 also initializes the switch ID table, generatesits new subject ID, and prohibits transmission of the table generatingframe from the switch 53. Then, the received initialization frame istransferred from the port P2 to the next switch 54.

Then, the switch 54 receives, from the port P2, the initialization frameincluding the new subject ID transmitted by itself (i.e., by the switch54), and performs the seventh process in FIG. 12 . Then, the switch 54determines “YES” in S810 of FIG. 12 and performs the process of S820 andS830. Therefore, the switch 54 stops the transmission of theinitialization frame, and transmits a table generating frame includingthe re-generated new subject ID as the sender MAC address from at leastone of the ring ports P1 and P2.

On the other hand, when the other switch 51 to 53 are respectivelyprohibiting the transmission of the table generating frame in responseto the reception of the initialization frame, the other switches 51 to53 perform the first process of FIG. 6 when receiving the tablegenerating frame from the switch 54 (i.e., the table generating framehaving the switch 54 as a sender). Then, the process of S240 and S250 isperformed by determining “NO” in S210 and S230 of FIG. 6 .

Therefore, the switches 51 to 53 permit and restart/resume thetransmission of the table generating frame, and perform the tablegeneration process of FIG. 5 . In such case, the switches 51 to 53determine “NO” in S120 of FIG. 5 and perform the process of S130 andS140.

Therefore, the table generating frame transmitted by the switch 54returns to the switch 54 after a round trip of the ring network, by theprocess of S130 and S140 in FIG. 5 performed by the switches 51 to 53.Then, the switch 54 generates the new switch ID table from the ID groupstored in the ID area of the table generating frame coming back from theround trip of the network.

Further, each of the other switches 51 to 53 also transmits the tablegenerating frame, and generates the new switch ID table from the IDgroup stored in the ID area of the table generating frame returned fromthe round trip/circulation of the ring network.

Here, when the switch 54 receives the table generating frame having theother switches 51 to 53 as a sender and performs the process of S130 inFIG. 5 , the switch 54 embeds, in the ID area of the received tablegenerating frame, the generated new subject ID. This also applies to theother switches 51 to 53. Therefore, the new switch ID tables of theswitches 51 to 54 are generated as recording the new IDs re-generated byrespective switches.

2-4. Effects

The second embodiment described above provides the effect (1a) accordingto the above described first embodiment and further provides thefollowing effects.

(2a) When it is determined that the switches 51 to 54 have beenrestarted from a reset, their new subject IDs are generated in S620 ofFIG. 10 . Then, among the switches 51 to 54, a switch restarted from areset generates its new subject ID, and subsequently transmits the tablegenerating frame including the new subject ID from at least one of thering ports P1 and P2 in S830 of FIG. 12 .

The table generating frame from the restarted switch goes around thering network while recording the IDs of the other switches respectivelyembedded by the other switches, and returns to the restarted switch.Then, the restarted switch generates the latest switch ID table andstores it in the memory 74 by the process of S150 in FIG. 5 .

Further, when the restarted switch receives the table generating framefrom the other sender after re-generating its subject ID, the restartedswitch embeds the re-generated new subject ID in S130 of FIG. 5 , in theID area of the table generating frame. Therefore, in the other switchthat is the sender of the table generating frame, a switch ID table inwhich the re-generated new ID is recorded as the ID of the restartedswitch is generated and stored in the memory 74.

Therefore, even if the ID and the switch ID table are lost due to thereset in any of the switches 51 to 54, a new ID is generated when therelevant switch is restarted. Further, in each of the other switches, aswitch ID table in which a new ID is recorded as the ID of the restartedswitch is generated, and in the restarted switch, a switch ID table inwhich the IDs of all of the other switches in the network are recordedis generated. Therefore, the switch ID table held by each of theswitches 51 to 54 is corrected.

(2b) When it is determined that the switches 51 to 54 have beenrestarted from the reset, before transmitting the table generatingframe, in S630 of FIG. 10 , the initialization frame including thegenerated new subject ID is transmitted from at least one of the ringports P1 and P2. Subsequently, when the initialization frame includingthe new subject ID is received from one of the ring ports P1 and P2, atable generating frame is transmitted in S830 of FIG. 12 .

Further, when the switch 51 to 54 receives the initialization frame fromthe other switch from one of the ring ports P1 and P2, the switch IDtable is initialized (i.e., deleted) in S840 of FIG. 12 , then, thetransmission of the table generating frame is prohibited in S860 of FIG.12 . Then, in S870 of FIG. 12 , the received initialization frame istransmitted from one of the ring port P1 or P2 that is different fromthe port that received the initialization frame. Subsequently,transmission of the table generating frame from the switch isrestarted/resumed on condition that the table generating frame isreceived. This transmission restart is performed by the process of S240in FIG. 6 .

Therefore, the switch restarted from a reset causes, by using theinitialization frame, the other switch to transmit the table generatingframe therefrom after causing the other switches (i) to perform aninitialization of the switch ID table and (ii) to prohibit thetransmission of the table generating frame. Then, by the transmissionthe table generating frame from the restarted switch, transmission ofthe table generating frame from the other switches is restarted.

Therefore, when any of the switches 51 to 54 is restarted from a reset,transmission of a table generating frame is firstly performed by theother switch, for generating the new switch ID table in each of theswitches 51 to 54. Then, in the switches other than the restartedswitch, the switch ID table is initialized by receiving theinitialization frame, and the new switch ID table is generated by thesubsequent transmission and reception of the table generating frame.Therefore, in the in-vehicle communication network system 1, it ispossible to suppress the mixture of the old and new switch ID tables,thereby securing/guaranteeing the accuracy of the process using theswitch ID tables.

(2c) Among the switches 51 to 54, the switch restarted from a resettransmits the initialization frame in S630 of FIG. 10 and subsequently,at regular intervals until the switch receives the initialization frametransmitted by the switch itself, keeps transmitting the sameinitialization frame in S720 of FIG. 11 . Therefore, the reachability ofthe initialization frame to the other switches can be increased.

(2d) When any of the switches 51 to 54 other than the switch restartedfrom the reset prohibits the transmission of the table generating frameby receiving the initialization frame, the switch restarts thetransmission of the table generating frame, even after “NO”determination in S910 of FIG. 13 . In other words, based not only on asatisfaction of a condition “the table generating frame is received fromthe other switch” but also on a satisfaction of a condition “theinitialization frame has not been received for the predetermined timeTs2 or more,” transmission of the table generating frame is restarted.Therefore, a situation in which transmission of the table generatingframe is kept/left prohibited is preventable.

In the second embodiment, S610 in FIG. 10 corresponds to a process as arestart determination unit. S620 and S630 in FIG. 10 , S710 and S720 inFIG. 11 , and S830 in FIG. 12 correspond to a process as a re-generationprocessing unit and a first re-generation processing unit. S840, S860,and S870 in FIG. 12 , S240 in FIG. 6 , and S920 in FIG. 13 correspond toa process as a second generation processing unit.

3. Other Embodiments

Although the embodiments of the present disclosure have been describedabove, the present disclosure is not limited to the embodimentsdescribed above, and various modifications can be made to implement thepresent disclosure.

For example, in the first embodiment, when the switches 51 to 54determine “NO” in S410 of FIG. 8 , that is, when receiving a duplicationnotification frame of the other sender (i.e., from the other switch),the switches 51 to 54 may perform one or both of the initialization ofthe switch ID table and the re-generation of the subject ID.

Further, for example, in the second embodiment, when receiving theinitialization frame from the restarted switch, the switches 51 to 54may keep using the subject ID already stored therein without performingthe process of S850 in FIG. 12 , that is, without re-generating theirsubject IDs. Further, in S130 of FIG. 5 , the ID embedded position inthe empty area of the ID area of the table generating frame is notlimited to the head of the empty area, but may be, for example, the endof the empty area. In such case, a plurality of IDs are sequentiallyembedded from the end toward the head of the ID area. Also, rules forhow to embed an ID into the empty area of the ID area (i.e., from whichposition toward which position) may be arbitrarily determined asappropriate.

The switches 51 to 54 and relevant methods described in the presentdisclosure may be implemented/realized by programming a special purposecomputer which is configured with a memory and a processor programmed toexecute one or more particular functions embodied as computer programs.Alternatively, the switches 51 to 54 described in the present disclosureand the method thereof may be realized by a special purpose computerconfigured as a processor having one or more dedicated hardware logiccircuits. Alternatively, the switches 51 to 54 and the method describedin the present disclosure may be realized by one or more special purposecomputers, which is a combination of (i) a programmable special purposecomputer having a processor and a memory, which are programmed toperform one or more functions, and (ii) a hardware-logic special purposecomputer having a processor with one or more hardware logic circuits.The computer programs may be stored, as instructions for performance bya computer, in a tangible, non-transitory computer-readable storagemedium. The technique for realizing the functions of each unit includedin the switches 51 to 54 does not necessarily need to include software,and all the functions may be realized using one or a plurality ofhardware.

In addition, multiple functions of one component in the above embodimentmay be realized by multiple components, or a function of one componentmay be realized by multiple components. In addition, multiple functionsof multiple components may be realized by one component, or a singlefunction realized by multiple components may be realized by onecomponent. In addition, a part of the configuration of the aboveembodiment may be omitted. Further, at least a part of the configurationof one of the above embodiments may be added to or substituted for theconfiguration of the other one of the above embodiments.

In addition to the switches 51 to 54 described above, the presentdisclosure can be realized in various forms, such as an in-vehiclecommunication network system including the switches 51 to 54 ascomponents, a program for causing a computer to function as the switches51 to 54, and a non-transitory, substantive memory medium such as asemiconductor memory storing the program, and a method of controlling arelay device.

What is claimed is:
 1. A relay device for use in a communication systemconfigured as a ring network of relay devices, the relay devicecomprising: a storage unit for storing connection information indicating(i) identification information of other relay device connected to asubject relay device in the ring network and (ii) a connection order ofthe other relay device as viewed from the relay device; and furthercomprising as functional units for generating the connectioninformation, a generating frame transmitter configured to transmit agenerating frame including the identification information of the subjectrelay device from at least one of two ring ports used for the ringnetwork among a plurality of ports (P1 to P4) provided in the subjectrelay device; a transfer processing unit, when receiving the generatingframe from the other relay device by any of the ring ports, configuredto transmit the received generating frame from a different one of thering ports by which the generating frame was received, after writing theidentification information of the subject relay device in an empty areaof an identification information storage area of the received generatingframe; a generating unit, when receiving the generating frame from thesubject relay device by any of the ring ports, configured to (a)generate the connection information based on (i) the identificationinformation of the other relay device embedded in the identificationinformation storage area of the received generating frame and (ii) anarrangement sequence of the written identification information and (b)store the generated connection information in the storage unit; aduplication determination unit configured to determine whether a relaydevice having the same identification information as the subject relaydevice exists in the communication system based on the receivedgenerating frame; a duplication elimination unit, when determined by theduplication determination unit that there is a duplication of theidentification information, configured to (a) generate newidentification information of the subject relay device, and subsequently(b) transmit the generating frame including the new identificationinformation from at least one of the ring ports, wherein the transferprocessing unit, after the new identification information is generatedby the duplication elimination unit, writes the new identificationinformation in the identification information storage area of thereceived generating frame.
 2. The relay device according to claim 1,wherein: the duplication elimination unit includes a first duplicationelimination unit, the first duplication elimination unit is configuredto transmit, when it is determined by the duplication determination unitthat there is a duplication, a duplication notification frame includingthe new identification information from at least one of the ring portsprior to transmission of the generating frame, and subsequently totransmit the generating frame when the duplication notification frameincluding the new identification information is received from any of thering ports, and the relay device includes a second duplicationelimination unit configured to, when the duplication notification framehaving an other relay device as a sender is received from any of thering ports: (i) prohibit the transmission of the generating frame by thegenerating frame transmitter and (ii) transmit the received duplicationnotification frame from a one of the ring ports that is different fromthe ring port receiving the generating frame, and subsequently (iii)restart the transmission of the generating frame by the generating frametransmitter on a condition that the generating frame is received fromany of the ring ports.
 3. The relay device according to claim 2, whereinthe first duplication elimination unit is configured to transmit theduplication notification frame including the new identificationinformation at regular intervals until the duplication notificationframe including the new identification information is received.
 4. Therelay device according to claim 3, wherein the second duplicationelimination unit, after prohibiting the transmission of the generatingframe, is configured to restart the transmission of the generating frameon a condition that (i) the generating frame is received from any of thering ports, or (ii) the duplication notification frame has not beenreceived for a period of the predetermined time or more.
 5. A relaydevice for use in a communication system configured as a ring network ofrelay devices, the relay device comprising: a storage unit for storingconnection information indicating (i) identification information ofother relay device connected to a subject relay device in a ring shapeand (ii) a connection order of the other relay device as viewed from therelay device; and further comprising as functional units for generatingthe connection information, a generating frame transmitter configured totransmit a generating frame including the identification information ofthe relay device from at least one of two ring ports used for the ringnetwork among a plurality of ports provided in the subject relay device;a transfer processing unit, when receiving the generating frame from theother relay device by any of the ring ports, configured to transmit thereceived generating frame from a different one of the ring ports bywhich the generating frame was received, after writing theidentification information of the subject relay device in an empty areaof an identification information storage area of the received generatingframe; a generating unit, when receiving the generating frame having thesubject relay device as a sender of the frame by any of the specificports, configured to (a) generate the connection information based on(i) the identification information of the other relay device written inthe identification information storage area of the received generatingframe and (ii) an arrangement sequence of the written identificationinformation and (b) store the generated connection information in thestorage unit; a restart determination unit configured to determinewhether the subject relay device has restarted from a reset; ageneration processing unit, when determined by the restart determinationunit that the subject relay device is restarted, configured to (a)generate new identification information of the subject relay device, andsubsequently (b) transmit the generating frame including the r newidentification information from at least one of the specific ports,wherein the transfer processing unit, after the identificationinformation is generated by the generation processing unit, embeds thenew identification information in the identification information storagearea of the received generating frame, wherein the generation processingunit includes a first generation processing unit, the first generationprocessing unit is, when it is determined by the restart determinationunit that a restart is performed, configured to (i) transmit theinitialization frame including the new identification information fromat least one of the ring ports prior to transmission of the generatingframe, and subsequently (ii) transmit the generating frame when theinitialization frame including the new identification information isreceived from any of the specific ports, and the relay device is furtherprovided with a second generation processing unit configured to, whenthe initialization frame having an other relay device as a sender isreceived from any of the specific ports, (i) delete the connectioninformation in the storage unit, (ii) prohibit the transmission of thegenerating frame by the generating frame transmitter, and (iii) transmitthe received initialization frame from the specific port, which isdifferent from the one from which the initialization frame was received,and subsequently (iv) restart the transmission of the generating frameby the generating frame transmitter on a condition that the generatingframe is received from any of the specific ports.
 6. The relay deviceaccording to claim 5, wherein the first regeneration processing unit isconfigured to transmit the initialization frame including the newidentification information at regular intervals until the initializationframe including the new identification information is received.
 7. Therelay device according to claim 6, wherein the second generationprocessing unit, after prohibiting the transmission of the generatingframe, is configured to restart the transmission of the generating frameon a condition that (i) the generating frame is received from any of thering ports, or (ii) the initialization frame has not been received for aperiod of the predetermined time or more.
 8. An in-vehicle communicationnetwork comprising: a relay device according to claim 1; and anelectronic control unit connected via a communication line to a normalport.
 9. A subject switch for use in a ring network including thesubject switch and at least two other switches, the switch comprising: acommunication controller; a first ring port; a second ring port; and amemory including: a media access control (MAC) address table, and aswitch identification (ID) table for storing at least a first connectionorder from one of the ring ports; wherein the subject switch isassociated with a subject switch ID and is configured to: generate atable generating frame including at least: a preamble in a first zone, adestination MAC address in a second zone, a sender MAC address in athird zone, a type in a fourth zone, data in a fifth zone, and a framecheck sequence (FCS) in a sixth zone; and transmit the table generatingframe; wherein the switch is further configured to: receive the tablegenerating frame; determine whether the sender MAC address in third zoneidentifies the subject switch; upon a determination that the sender MACaddress in third zone identifies the subject switch, generate new switchidentification table; and upon a determination that the sender MACaddress in the third zone does not identify the subject switch, (i)write the subject switch ID in an empty area of an ID area in the fifthzone to modify the table generation frame, then (ii) transfer themodified table generation frame to a next switch of the other switcher,further configured to perform a first process determining whetherduplication occurs, wherein: upon a determining that a first conditionis satisfied and a second condition is satisfied, then the switchperforms a first series of steps; upon determining that a thirdcondition is satisfied, then the switch performs the first series ofsteps; upon a determination that the third condition is not satisfied,then the switch performs a second series of steps; the first conditiondetermines whether the sender MAC address in the third zone includes thesubject switch ID; the second condition determines whether the ID areain the fifth zone is empty; the third condition determines whether thesubject switch ID is stored in the ID area of the fifth zone; the firstseries of steps includes: prohibit transfer of any table generatingframe, initialize the switch identification table, generate a newsubject ID, and transfer a duplication notification frame including thenew subject ID as a sender MAC address in the duplication notificationframe; and the second series of steps includes: permit transfer of thetable generating frame, and perform the table generating process. 10.The switch of claim 9, further configured to perform a second processincluding: determine whether a received duplication notification frameincludes the subject switch ID; upon determining that the receivedduplication notification frame does not include the subject switch ID,then transmit the duplication notification frame.